This invention relates to fuel injection pumps for multi-cylinder internal combustion engines, and more particularly to a fuel cut-off device for fuel injection pumps of this type.
It has conventionally been carried out to cut off the supply of fuel to preselected cylinders of a multi-cylinder internal combustion engine to interrupt fuel injection into these cylinders during operation of the engine, for so-called "partial cylinder operation" during low speed running or for use of the cylinders as compressors for supplying compressed air. For instance, at engine idle, the partial cylinder operation is carried out wherein the supply of fuel to part of the cylinders is cut off so as to supply the other operating cylinders with an adequate amount of fuel in order to achieve stable idling operation of the engine as well as improved emission characteristics of same. Further, if carried out during low load operation such as running on a downward slope or low speed running during a traffic jam, the partial cylinder operation of an automobile engine will enable saving the fuel cost, contributing to the recent demand for energy saving. As another example, the fuel-cut cylinders are used as compressors to utilize the resultant compressed air for transferring fodder from a fodder tank in a silo to a transport container, etc.
A conventional typical fuel cut-off device of this kind is constructed as follows: A fuel feeding line is divided into a first portion connected to a group of fuel injection units to be subjected to cutting-off of fuel, and a second portion connected to another group of fuel injection units to be permently supplied with fuel during operation. A fuel cut-off valve is arranged across the first portion of the fuel feeding line at a location upstream of the first group of fuel injection units, which is closed when it is required to cut off the supply of fuel to the same group of fuel injection units.
However, since the fuel cut-off valve is arranged upstream of the fuel injection units to be subjected to cutting-off of fuel as above, the fuel injection does not terminate until all the fuel within the fuel injection units is injected after closing of the fuel cut-off valve. Also, when the fuel cut-off valve is opened to resume or start the fuel injection, the fuel injection does not start until after fuel has been supplied into the fuel injection units to a sufficient amount after the opening of the fuel cut-off valve.